The invention generally relates to a low-voltage circuit breaker with an arc extinguishing chamber and with a switching gas damper for absorbing switching gases which emerge from the arc extinguishing chamber. The switching gas damper is preferably detachably mounted on the circuit breaker and has an inlet opening for switching gases which emerge from an outlet opening in the arc extinguishing chamber.
A low-voltage circuit breaker is disclosed in DE 35 41 514 C2, with one switching gas damper in each case being provided for each extinguishing chamber of the circuit breaker. EP 0437 151 B1 similarly discloses a switching gas damper of the stated type, which is shared by the extinguishing chambers of a multipole circuit breaker.
A reasonable volume and materials or inserts which are accommodated in the enclosure of the switching gas damper, cool the switching gases and influence their flow are essential for the effect of the known switching gas dampers.
An embodiment of the invention may be based on an object of providing a switching gas damper with as small a volume as possible and which is more effective.
According to an embodiment of the invention, this object may be achieved in that the enclosure of the switching gas damper includes two body elements which are guided such that they can move relative to one another, of which a first body element is fitted to the circuit breaker and the other body element can be moved against an elastic restoring force relative to the first body element in order to enlarge the internal area which is enclosed by the body elements.
The elastic restoring force has the effect that it is possible to enlarge the internal area of the switching gas damper, starting from a relatively small initial size, under the influence of the switching gases. The switching gas damper thus forms a breathing buffer which is automatically matched to the respectively produced amount of switching gases. DE 196 38 948 A1 has already, per se, disclosed a switching gas damper with an enclosure which comprises body elements which are guided such that they can move relative to one another. However, this switching gas damper is not mounted on the circuit breaker but is fitted to an insert frame, and thus engages with the arc extinguishing chambers only when the circuit breaker is pushed in. With regard to the pressure of switching gases, this switching gas damper behaves rigidly, in the same way as the known switching gas dampers mentioned initially (DE 35 41 514 C2 and EP 0 437 151 B1), because the capability of the body elements to move relative to one another is provided only for tolerance compensation and for sealing between the fixed-position switching gas damper and the moveable circuit breaker.
The xe2x80x9cbreathingxe2x80x9d method of operation of the switching gas damper according to an embodiment of the invention allows different functions, which can be used as required. In particular, the switching gas damper can form a closed system together with the circuit breaker. On the other hand, it may be advantageous for the switching gas damper to have an outlet opening for switching gases, which can be opened by a relative movement of the body elements. After the end of a switching process, the body elements of the switching gas damper return to their basic position, in which the outlet opening is closed.
Both for a xe2x80x9cclosedxe2x80x9d and for an xe2x80x9copenxe2x80x9d configuration of the switching gas damper, it has been found to be advantageous for the body elements of the switching gas damper to be designed such that they engage in one another telescopically, as is already known per se. In particular, the capability to move telescopically allows advantageous embodiments of outlet openings. In one of these embodiments, edge areas of the mutually overlapping walls of the body elements can be provided with inclined surfaces in the same sense in order to form outlet openings which are aligned at least partially parallel to the walls. Any gas which emerges thus emerges at an angle to the side walls of the circuit breaker, in contrast to a flow which was previously directed directly upward or at right angles to the side.
In a further advantageous embodiment of a switching gas damper, outlet openings are formed by providing the walls of the body elements of the switching gas damper with openings which do not correspond to one another when the body elements are in the basic position and correspond to one another partially or entirely when the body elements are moved relative to one another. This results in a diffuse flow.
The effect of the switching gas damper as a buffer can be further increased by the switching gas damper containing a porous material which can absorb switching gases. A material such as this, preferably of a mineral or metallic nature, provides protection against fluctuations or oscillations of the gas pressure, which may cause undesirable reactions on the extinguishing of the switching arc in the arc extinguishing chamber of the circuit breaker.
The elastic restoring force which acts between the body elements of the switching gas damper can expediently be applied by arranging opposing bearings, which originate from the body elements, for a spring which prestresses the body elements with respect to one another, in the internal area of the switching gas damper, and providing a stop in order to limit the relative movement of the body elements. Although an arrangement of springs such as this is similar to one embodiment of the switching gas damper according to the initially cited DE 196 38 948 A1, the direction in which it acts is actually reversed since, in the context of the invention, the body elements are drawn together and are not spread apart from one another.
With regard to the desired compact structure of the circuit breaker and of the switching gas damper, difficulties arise in arranging said springs sufficiently far away from the inlet opening to preclude contact with corrosive switching gases. According to one development of the invention, this problem can be avoided by at least one of the opposing bearings being designed as a protection body which shields the spring from the internal area of the switching gas damper.
Although the arrangement of outlet openings explained above intrinsically ensures limited relative movement between the body elements, it is recommended, according to a further embodiment of the invention, that the opposing bearings are at the same time to be designed as a stop in order to limit the relative movement of the body elements. This fixes the height of the installation area in the circuit breaker.